This invention relates to a device for joining a plurality of light-transmitting optical materials.
In making an optical device by joining a plurality of light-transmissive optical materials, a transparent adhesive is conventionally used to join the optical materials together.
It is known in the art that, when a light beam strikes the interface between two substances of different refractive index, Fresnel reflection occurs at the interface.
In an optical device which, as shown in FIG. 9, uses one optical material having a refractive index n.sub.0 joined to another optical material having a refractive index n.sub.1, the Fresnel reflection factor R of a vertical incident light beam is as follows: EQU R=(n.sub.1 -n.sub.0).sup.2 /(n.sub.1 +n.sub.0).sup.2 ( 1)
Accordingly, if the refractive index n.sub.0 of an adhesive used to join optical materials is different from that n.sub.1 of the optical material, Fresnel reflection represented by equation (1) results with respect to incident light.
In general, light-transmissive dielectric crystals such as LiNbO.sub.3, LiTaO.sub.3, TeO.sub.2 or PbMoO.sub.4 have relatively large refractive indexes of greater than 2. On the other hand, the refractive index of commonly used transparent adhesives is about 1.5. Therefore, in the interface between the dielectric crystal and the transparent adhesive layer, Fresnel reflection of more than 2% is produced.
The intensity of the signal light in an optical device comprising a plurality of joined, light-transmissive optical materials is decreased when Fresnel reflection occurs. Furthermore, Fresnel reflected light interferes with light beams reflected from the other surfaces, resulting in unwanted interference fringes. As a result, Fresnel reflected light decreases the contrast of the signal light in an optical device.
Accordingly, it is an object of the present invention to provide an optical device comprising a plurality of light-transmissive optical materials joined together by means of transparent adhesive film layers, in which Fresnel reflection at the interface between adjacent optical materials is substantially prevented.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in appended claims.